The controlled disproportionation of metastable Al I halide solutions has been developed into a fruitful concept for the generation of metalloid Al cluster compounds as intermediates on the way to bulk phases of Al metal during the last years [Eq. (1), X = Cl, Br, I]. [1] 3 AlX ! 2 Al metal þ AlX 3 ð1Þ

Dedicated to Professor Helge Willner on the occasion of his 60th birthdayDepicting the electronic structure of compounds clearly is one of the most difficult tasks in chemistry. For molecular moieties of identical atoms (clusters) many models have been developed which are often limited to specific compound classes. Gaseous cluster species, for example, as ions in mass spectrometry, could suitably be described with the Jellium model because the filling of electronic shells in these species, like in atoms, with specific numbers of valence electrons can explain their different stabilities.[ (Figure 1). [6,7] The rules of Wade, [9] Mingos, [10] Zintl, [11] Klemm, [11] and Jemmis, [12] for example, were useful in the explanation of bonding found in the structurally characterized cluster species of boranes or Zintl ions. But these models can only rudimentarily be applied to larger cluster species of identical metal atoms [13] (for example [Al 77 R 20 ] 2À ). The topological similarity in the arrangement of metal atoms of these clusters with the one found in elements was our motivation for terming such species metalloid or even elementoid clusters. [14,15] Recently King and Schleyer could show that some of the mentioned rules can in fact be used in the bond description of such a metalloid [Ga 22 R 8 ] cluster (Figure 1). [16] Herein, we attempt to demonstrate that the Jellium model can also contribute to the understanding of several metalloid clusters. These considerations are now possible for the first time because a unique possibility of comparison for a single element is given by a {Ga 23 } cluster presented here and four further differently structured {Ga 22 } clusters, [17] as well as a recently reported {Ga 24 } cluster [8] (Figure 1). The capacity of the Jellium model to describe the bonding of such clusters can be assessed based on experimental structural data. For the discussion on the bonding situation special attention will be given to the atomic volumes.At À78 8C a suspension of LiN(SiMe 3 ) 2 in toluene was treated with a small excess of a metastable GaCl solution in toluene/ether (3:1) that was obtained by the joint condensation of GaCl molecules formed at about 900 8C and the solvent mixture.[18] After processing the reaction solution (see the Experimental Section) black rhombus-shaped crystals of the title compound [Ga 23 {N(SiMe 3 ) 2 } 11 ] (1) were obtained. [19] Thus, formally, disproportionation and subsequent or simultaneous metathesis of GaCl occurred in the reaction.The result of the X-ray structural analysis of 1 is presented in Figure 2 a.[20] A body-centered naked {Ga 12 } core is present in 1 and is surrounded by 11 GaR moieties. The most important structural data are shown in the caption of Figure 2, where 1 is contrasted with the similar cluster [Ga 22 {N(SiMe 3 ) 2 } 10 ] 2À (2).[21] Both clusters contain a central Ga atom uncommonly surrounded by 11 further "naked" (that is, not ligand-bearing) gallium atoms.[22] The ligand shell of 1 is formed by 11 GaR moieties, and that of 2 is for...

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Die kontrollierte Disproportionierung von metastabilen AlIHalogenid-Lösungen hat sich in den letzten Jahren zu einer erfolgreichen Strategie für die Herstellung von metalloiden Al-Clusterverbindungen als Zwischenstufen auf dem Weg zu Aluminiummetall-Volumenphasen entwickelt [Gl. (1), X = Cl, Br, I]. [1] 3 AlX ! 2 Al metal þ AlX 3 ð1ÞUm die thermodynamisch bevorzugte Metallbildung zu verhindern, werden die Halogenidliganden -parallel zur Disproportionierungsreaktion -durch sperrige Liganden substituiert. Die Mehrzahl der metalloiden Al-Cluster, die in unserer Arbeitsgruppe hergestellt wurden, ist durch N(SiMe 3 ) 2 -Liganden geschützt.[1] Hier stellen wir einen großen metalloiden Al-Cluster vor, der ausschließlich aus Al-, C-und H-Atomen aufgebaut ist.

Cluster on cluster: [Ga12Ga12(Br18Se2)]⋅12 THF units with a platonic polyhedral substructure are ordered through the crystal in straight lines by SeSe contacts in an arrangement resembling superatoms (see picture). According to topological, spectroscopic, and energetic findings, these chains of clusters can be interpreted as a model for the lattice structure of photoconducting GaSe.

Dedicated to Professor Heiko Lueken on the occasion of his 65th birthdaySome years ago we established the developing area of metalloid Al clusters with the cluster ion [Al 7 R 6 ] À (1, R = N(SiMe 3 ) 2 ). [1][2][3][4] The topology of the seven Al atoms in the form of two vertex-sharing tetrahedral {Al 4 } moieties is unique for metal atom clusters and has raised the still unanswered question: Can the central "naked" Al atom with its six directly bound neighbors be regarded as a section of the face-centered cubic (fcc) structure of solid aluminum, that is, the basic form of metalloid clusters, or is it better understood as an Al 3+ ion stabilized by two aromatic {Al 3 R 3 } 2À moieties in a sandwich-type arrangement as in the aluminocenium cation [AlCp* 2 ] + , prepared by us for the first time (Cp* = C 5 Me 5 )? [5] In the meantime, we could demonstrate for further substituted [Al 7 R 6 ] À clusters (R = N(SiMe 2 R'), R' = hexyl, Bu, iPr)[6] that these {Al 7 } clusters are evidently energetically favored in their monoanion form. In an attempt to answer the question concerning the bond situation, we varied the synthesis with the aim of isolating neutral [Al 7 R 6 ] species and obtained the cluster radical [Al 7 R 6 ] (2, R = N(SiMe 2 Ph) 2 ). The experimentally determined changes in structure between 1 and 2 and additional DFT calculations allow a first approach towards understanding the complicated bonding situation for clusters with such a prototypical {Al 7 } framework.

Towards the Understanding of the Unexpected Properties of the Metalloid Cluster Compound [Ga84(N(SiMe3)2)20][Li6Br2(THF)20]·2ToluolIn several short communications we have recently reported on the electrical and superconducting properties of the crystalline title compound 1 which contains anionic Ga84R20‐moieties.Here we present a collection of these results, complemented and interpreted by using DFT‐calculations on model clusters (Ga84(NH2)20−). These calculations allowa) a first insight into the dynamics of the Ga84‐moieties (e.g. a rotation of the central Ga2‐dumbbell) and thus an explanation of the temperature‐dependent Ga‐NMR‐spectra described recently, andb) estimations on the lattice energy of 1 and its resulting unexpected energetic stabilization compared to metallic gallium. A possible contribution of the cations in the electrical conduction mechanism of 1 can also be made feasible with model calculations.The basis for all the results presented is to be found in the “perfect” arrangement of nanoscopic Ga84‐clusters in the crystal. This theoretically predicted condition for superconductivity in a “chain” of identical metal cluster molecules is a requirement which can hardly be realized by means of physical fabrication methods. Therefore, on the one hand the results presented here make for some disillusionment in the field of nanoscience, but on the other hand, especially in the field of synthetic chemistry, they present rewarding challenges for fundamental work in the future.

We report muon-spin-relaxation studies in weak transverse fields of the superconductivity in the metal cluster compound, Ga84[N(SiMe3)2]20-Li6Br2(thf)20.2 toluene. The temperature and field dependence of the muon-spin-relaxation rate and Knight shift clearly evidence type II bulk superconductivity below Tc approximately 7.8 K, with Bc1 approximately 0.06 T, Bc2 approximately 0.26 T, kappa approximately 2, and weak flux pinning. The data are well described by the s-wave BCS model with weak electron-phonon coupling in the clean limit. A qualitative explanation for the conduction mechanism in this novel type of narrow-band superconductor is presented.